The Moon's Permanently Shadowed Regions

Image Credit:
NASA's Goddard Space Flight Center

Published:
March 6, 2013

As you watch the Moon over the course of a month, you'll notice that different features are illuminated by the Sun at different times. However, there are some parts of the Moon that never see sunlight. These areas are called permanently shadowed regions, and they appear dark because unlike on the Earth, the axis of the Moon is nearly perpendicular to the direction of the sun's light. The result is that the bottoms of certain craters are never pointed toward the Sun, with some remaining dark for over two billion years. However, thanks to new data from NASA's Lunar Reconnaissance Orbiter, we can now see into these dark craters in incredible detail.

As you watch the Moon over the course of a month, you'll notice that different features are illuminated by the Sun at different times. However, there are some parts of the Moon that never see sunlight. These areas are called permanently shadowed regions, and they appear dark because unlike on the Earth, the axis of the Moon is nearly perpendicular to the direction of the Sun's light. The result is that the bottoms of certain craters, like here at the Moon's south pole, are never pointed toward the Sun, with some remaining dark for over two billion years.

However, thanks to new data from NASA's Lunar Reconnaissance Orbiter, we can now see into these dark craters in incredible detail. Seeing the shape of the crater is important, and LRO has used its LOLA instrument to make the best yet topographical maps of these craters by reflecting lasers off the lunar surface. This has allowed us to see the shapes of the craters' interiors from any angle, and by making 3D models, we can light up the crater floors as if we had a giant flashlight. And although the Sun never illuminates these craters, other stars still cast a faint light into the permanent shadows. LRO's LAMP instrument can actually measure this light, giving us yet another view of this unique region on the Moon.

LRO's DIVINER instrument can also measure temperature, revealing the extreme cold within the craters.

Finally, LRO's LEND instrument can measure the speed of neutrons to detect elements like hydrogen in the lunar soil.

So, while there are some areas on the Moon that never see the light of day, LRO will keep collecting data so that we can learn more about them. And as we continue to study the Moon, we'll improve our understanding of Earth's original satellite, and, pun fully intended, bring new discoveries to light.